The long term goal of my research is to define in molecular detail the factors that control embryonic cell motility. Here I propose to use melanocytes as a model system with which to address some fundamental questions concerning cell migration in the embryo. Specific aims are: 1) To determine when and where melanoblasts form, using markers that recognize the earliest stages of melanogenesis. Available markers include TRP-2 (tyrosinase associated protein-2) and an antiserum derived from Smyth line chickens. Our hypothesis is that those neural crest cells that are arrested at the entrance to the dorsolateral path become specified as melanocyte precursors. 2) To determine what molecular changes occur in melanoblasts that confer upon them the ability to migrate in the dorsolateral path. We will challenge three hypotheses: i)melanoblasts acquire sensitivity to a chemotactic source that attracts them to the dermis. We will explore specifically whether Steel factor acts as the chemotactic cue; ii)melanoblasts acquire the ability to migrate in the previously inhibitory dorsolateral path owing to changes in the repertoire of integrins that they express; iii)the migratory substratum of the dorsolateral path changes, entailing either a loss of an inhibitory cue, such as chondroitin sulfate proteoglycan, or the deposition of a permissive cue, such as Steel factor, which we predict could function as an adhesive substratum. 3) To determine what environmental cues control melanogenesis. We hypothesize that growth factors near the dorsal neural tube and dermatome regulate melanoblast specification, differentiation and/or survival. We will specifically examine the role of Steel factor in these events. We will use chicken and quail embryos as our experimental model system. Birds provide several advantages over mice, which have been employed most recently to study melanogenesis: 1) We can purify large numbers of avian melanocytes as well as melanoblasts in various stages of differentiation. 2) We can culture avian neural crest cells more readily than murine crest, allowing for direct observation and manipulation of melanoblasts in vitro. 3) Chicken embryos are more amenable to experimental manipulation and lineage tracing. 4) Finally, avian pigment mutants, such as the Silkie strain, will permit alternative means with which to test our hypotheses. Given the exceptional invasive capabilities of melanocytes, these experiments will also shed light on the molecular changes that result in embryonic cell motility and in invasion and metastasis in pathological conditions such as cancer.